From my understanding so long as the marriage was properly registered by a registrar in Gibraltar it will be registered in the UK if you are a British National. You can make sure by checking the records of Births, Marriages and Deaths in the UK online.

Well it seems to be a dilemma on my behalf, as I got married in Gibraltar, divorced in Tenerife (Spain) and just some years ago my x wife passed away, and I'm now considering marrying again.. as such I believe I need to obtain a certificate decree of absolute, now based in the UK will be somewhat difficult to get that certificate.